The invention relates to a display device comprising a display screen, a surface of which is provided with an anti-reflection filter having a conducting layer comprising metallic particles and transparent areas, the conducting layer being provided with a transparent layer. The invention also relates to a picture display apparatus.
WO 98/49707 describes a display device provided with an anti-static and anti-reflection filter. Such a filter has a conducting layer which comprises metal particles and transparent particles shielded by a further transparent layer. The metal particles provide for the conductance and the transparent particles provide for the transmission of light. The assembly of the conducting and shielding transparent layer has a very low reflection. Such filters are provided on the display screen of a display device, for example, on cathode ray tubes or a plasma display panel (PDP).
For use of a display device as a computer monitor, where the user is relatively close to the display screen, the display device must satisfy stringent standards relating to the so-called AEF field (Alternating Electric Field). The AEF field is an unwanted electromagnetic field which should have a minimal intensity. The AEF field can be reduced by providing the display screen with an electrically conducting layer which is at ground potential.
It is an object of the invention to provide a display device with a reduced AEF field. To this end, the display device according to the invention is characterized in that the transparent layer has a thickness (d2) which is smaller than or equal to the thickness (d1) of the conducting layer, the thickness of each layer (d1, d2) being measured from the surface of the display screen up to the upper side of the layer, the display screen being provided with at least one electrically conducting strip comprising a metal layer and an adhesive layer provided with electrically conducting particles, the electrically conducting strip being in local electrical contact with the metallic particles of the anti-reflection filter via the conducting particles of the adhesive layer.
The invention is also based on the recognition that, for a satisfactory shielding effect, it is of great importance to obtain a satisfactory electrical contact between the electrically conducting layer and the ground potential contact. The invention realizes a satisfactory electrical contact between the electrically conducting layer and the ground potential contact.
Practice has proved that larger clusters of metal particles comprised in the conducting layer of the anti-reflection filter protrude from the transparent layer. The inventors have recognized that this property provides an elegant possibility of preventing or reducing possible AEF fields. This is realized by providing one or more special conducting strips on the screen. A satisfactory electrical contact between the strip and the metal clusters is obtained by making use of a conducting strip which comprises a metal layer and an adhesive layer provided with electrically conducting particles. Due to these measures, a display screen is obtained in which a satisfactory electrical contact is realized between the electrically conducting layer and the ground potential contact.
The use of metal strips to prevent AEF fields is known per se from the English language abstract of Japanese patent application JP-A 04-249036. This document describes a display device with a display screen provided with a transparent electrically conducting layer. Strips of a metal foil which are in contact with the rim band provided around the screen and connected to earth are provided on the transparent layer. The electrical resistance of the electrically conducting layer must be as low as possible, for example, lower than 1000 ohm/square. Such conducting layers are usually provided on the display screen by means of a wet-chemical method in the final stage of the display tube production, in which a temperature step of maximally only 160xc2x0 C. is allowed. As a result, layers having such a low resistance are difficult to manufacture and, moreover, are comparatively expensive. The above-mentioned abstract does not disclose the structure of the electrically conducting layer, nor does it disclose anything about the construction of the metal strips.
An embodiment of the electrically conducting strip is characterized in that at least 2% of the volume of the adhesive layer is filled with the electrically conducting particles. It has been found by experiments that, at such a value of the volume density, a good contact is obtained between the electrically conducting strip and the electrically conducting layer on the display screen.
An embodiment of the electrically conducting strip is characterized in that at least 30% of the volume of the adhesive layer is filled with the electrically conducting particles. It has been found by further experiments that, at such a value of the volume density, a good contact is obtained between the electrically conducting strip and the electrically conducting layer on the display screen.
An embodiment of the electrically conducting strip is characterized in that the strip has a width which is larger than or equal to 0.3 cm. It has been found that strips with such a width have a good conductivity, so that it is possible to reduce the number of required strips to only two or three. This results in a further reduction of costs.
An embodiment of the display device comprises a funnel-shaped portion which is secured to the display screen, which funnel-shaped portion is at least partly provided with an electrically conducting layer, and is characterized in that the conducting strip is also in electrical contact with the electrically conducting layer. In this embodiment, the customary means for bringing the electrically conducting layer to ground potential such as, for example, wire constructions can be dispensed with. This reduces the costs of the display device.
A second aspect of the invention relates to a display apparatus comprising means for generating a picture signal, and a display device as described hereinbefore for displaying the picture signal.
These and other aspects of the invention are apparent from and will be elucidated with reference to the embodiments described hereinafter.